Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 171100 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 600 AM EST Wed Jan 17 2018 .SYNOPSIS... Low pressure will move into the Canadian Maritimes today. High pressure will build across the Gulf coast through the end of the week, then offshore over the weekend. An area of low pressure will move across eastern Canada over the weekend as a back door cold front approaches from the north. Another area of low pressure will move through the Great Lakes Monday night into Tuesday, pulling a cold front across the area. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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We extended the Winter Weather Advisory until 9:00 AM for upper Bucks County based on the latest trends. The remainder of the Winter Weather Advisory and the Winter Storm Warning continues to look reasonable. A cold front passed through our region from west to east early this morning. Meanwhile, low pressure was off the New Jersey coast. The low will move northeastward and it should reach the waters east of New England this afternoon. Snow was falling in much of eastern Pennsylvania, northern New Jersey and along the Interstate 95 corridor in our region around 5:45 AM. Light rain was occurring in southeastern and far southern New Jersey. The boundary layer will continue to cool and the rain will change to snow early this morning. The steady snow is expected to end gradually across our forecast area from west to east between about 7:00 and 11:00 AM. However, some light snow may linger a little beyond 11:00 AM, especially in northern New Jersey and in areas near the coast. The storm total snowfall amounts should range from up to an inch in the Philadelphia metropolitan area and in parts of southern New Jersey to around 6 inches in the elevated terrain of the Poconos and northwestern New Jersey. Temperatures are not expected to recover much today as cold air builds into our region on a northwest wind. Wind speeds are forecast to increase to 10 to 15 MPH with gusts around 20 MPH.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/... The low is forecast to move across Canada`s Maritime Provinces tonight as high pressure begins to nose into our region from the west and southwest. We are anticipating a mostly clear sky along with a northwest to west wind around 5 to 10 MPH. Cold temperatures will return for tonight with lows mostly in the teens. Single digit readings are possible in the Poconos and in far northern New Jersey. && .LONG TERM /THURSDAY THROUGH TUESDAY/... Main focus of the long term is the warmup late this week through this weekend and a storm system moving through the region early next week. Most of the focus today was on the first 36 hours of the forecast, so overall made few changes from the previous shift. Trough axis swings through the Eastern Seaboard Wednesday night, with a broad surface high building into the Mid-Atlantic and Southeast for the rest of the week into the weekend. After a small- scale perturbation moves through the Northeast Thursday night (which should be dry), midlevel zonal flow will be present Friday through the weekend, allowing the surface high to slide eastward and promoting southwesterly surface flow to develop east of the Appalachians this weekend. This pattern will result in a lengthy dry period and a distinct warming trend after a chilly Thursday (when heights/thicknesses will be lowest, owing to the proximity of the trough). Forecast highs are in the 50s for Philly this weekend, based on a consensus blend of statistical guidance...though I leaned a little on the higher side of consensus given the tendency for MOS to be on the low side in warming patterns. Operational models develop a strong surface cyclone in the central plains this weekend (with downstream ridging further contributing to warmth Sunday and Monday in our area) before lifting it rapidly northeastward into the Great Lakes and adjacent southeast Canada early next week. A strong cold front will progress through the East Monday and Tuesday, with showery precipitation developing near the front. Temperatures will likely be warm enough for liquid in most locations for the event, with the exception being the far northwest CWA during the precip`s waning stages. Regarding timing, models generally agree on Monday afternoon through Monday night. Given such good agreement this far out, boosted PoPs to high chance or likely during this time frame. The greater uncertainty lies with the intensity of the precipitation (given the southern origins of the system and the warmth it advects downstream, there is some potential for decent precipitation totals, especially if embedded convection can develop), extent of cold air on the upstream side of the system (i.e., precipitation type issues as the system departs), and the speed with which the precipitation moves out before the colder air moves in. As previously mentioned, did not change the details during this time frame too much, but my initial thoughts were to go on the warm side and on the quick side given typical model biases with northeast- progressing inland surface lows originating from the southern/southwestern U.S. By midweek, temperatures will be slightly cooler, and conditions should dry out. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...IFR and MVFR conditions this morning improving to VFR for the afternoon. The snow is forecast to end from west to east between about 1100Z and 1500Z in our region. We are expecting a northwest wind around 10 to 12 knots gusting near 20 knots. Tonight...VFR with a mostly clear sky and a northwest to west wind at 5 to 10 knots. OUTLOOK... Thursday through Sunday...VFR. West to southwest winds; winds may gust 15-20 knots at time. High confidence. && .MARINE... A northwest wind is expected to increase to 15 to 20 knots today with gusts of 25 to 30 knots. As a result, a Small Craft Advisory is in effect for today and tonight. OUTLOOK... Thursday...Small Craft Advisory extended through the day Thursday as winds expected to gust to 25 knots. Thursday night...Conditions expected to drop below advisory levels. Friday-Sunday...Conditions expected to remain below advisory levels, but winds may periodically gust around 20 knots. && .EQUIPMENT... Sudlersville NWR conts off the air overnight. RDG temp turned off and our ET staff hopefully can resolve tomorrow. Data went bad in a gradual fashion beginning ard 2325z. PTW and GED have FAA comms issues. && .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...Winter Storm Warning until 11 AM EST this morning for PAZ054- 055. Winter Weather Advisory until 11 AM EST this morning for PAZ062. Winter Weather Advisory until 9 AM EST this morning for PAZ105. Winter Weather Advisory until 7 AM EST this morning for PAZ060- 061-101-103. NJ...Winter Weather Advisory until noon EST today for NJZ008>010. Winter Storm Warning until 11 AM EST this morning for NJZ001. Winter Weather Advisory until 11 AM EST this morning for NJZ007. DE...None. MD...None. MARINE...Small Craft Advisory until 6 PM EST Thursday for ANZ450>455. Small Craft Advisory from 9 AM this morning to 10 AM EST Thursday for ANZ430-431.
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&& $$ Synopsis...Robertson Near Term...Iovino Short Term...Iovino Long Term...CMS/Robertson Aviation...Iovino/Robertson Marine...Iovino/Robertson Equipment...Drag

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